ECN Forum Forums General Topics of the Trade Voice - Data - Video Discussion Basic Coax TV Cable Questions

The thinnet specification calls for an RG-58 cable with a stranded center conductor and a 95% or better shield.

Most RG-58 I've seen has a solid center conductor. The few RG-58 cables I've seen with a stranded center conductor were specifically identified on the jacket as being for IEEE 802.3 10base2.

Just regarding the cascading of splitters.
You can get 6 way:



And even 8 way types:



Just bear in mind that with the more ports you have, the higher the losses will be.

Scott35,
I think you may be referring to Air-spaced RG-59/U coax, it used to be used here quite a bit for TV aerials and the like.
The air-spacing gives a lower attenuation figure than the standard solid polyethylene insulation.
Hmm, RG-7, can't say I've ever struck that one before.


[This message has been edited by Trumpy (edited 05-24-2005).]

A 2-way splitter has 3.5dB of loss.

A 4-way splitter, 7dB.

An 8-way splitter, 11.5dB.

(3-way splitters have a loss that varies depending on which output you are looking at. Two outputs are 3.5dB and one is 7dB of loss, unless you have one of the exceedingly rare equal-loss 3-way splitters. I've never seen one and offhand I don't recall what the loss is for those).

Simply add up the loss of all the splitters in the signal path to get the total loss, and if you are dealing with very long runs of cable you could add in the cable loss too.

Most cable companies seem to feed houses with a signal level adequate for at least a 4-way splitter. My cable company feeds my house with about 14dBmV, so I could use an 8-way splitter to hook up 8 TVs and still have an adequate signal.

You do not want the signal level to drop below 0dBmV because that is generally considered the minimum signal level which will produce a picture with no visible defects. Cable modems will be OK with lower levels, although they suggest no lower than negative 15dBmV. In fact, my brother has a cable modem connected through a 4-way and a 2-way splitter totalling 11.5dB of splitter loss and it works fine. Unfortunately I can't find out how to access the diagnostic webpage for that modem, I'd really like to know what sort of signal level it's getting.
(On top of the splitter loss, there's the cable loss..there's got to be at least 150' of cable between the cable tv pedestal and that cable modem).


[This message has been edited by brianl703 (edited 05-24-2005).]

I think the 3-output splitter would be 2 outputs at 7 dB down, and one at 3.5.

The rule of thumb is 3.5db per split (although large ones will deviate from this slightly) and consider that all splitters are cascaded 2-ways in the same can. Applying that to a 3-way, it would be two 2-ways in the same can. That is why two outputs are -7db and the other -3.5. We call that the hot leg or hot port.

-Hal

Yes, I was mistaken about that.That's what I get for posting late at night.

Romex Racer, a cheapo way to test tv cables before customer shows up on site is a dvd player set up at the demarcation spot, and one of those really small b+w sets with the tiny screens. If the picture is sharp, your cables and connectors are also.

That may not find all potential problems with the installation.

In particular, unless there is a strong over-the-air signal on channel 3 or 4 (depending on which you are using to test), the picture could look fine even if your installation has an ingress (the cable allowing external signal to leak into it) problem.

Ingress problems usually show up on cable channels 17, 18, and 19 as an intermittent herringbone pattern because the frquencies used correspond with those used over-the-air for pagers, and the pager signals are quite strong.

I wonder if you could use a radio scanner to test your installation for ingress: Connect it to one of the drops with a BNC-to-F adapator and then terminate the other end of the drop with a 75-ohm terminator. Then see if it picks up anything on the paging frequencies used in your area.

This would depend on how well-shielded the scanner itself is, however. That can be tested by terminating it's antenna input with a terminator and seeing whether it picks up any paging signals.

Well guys, I know you sometimes want to test your work before the customer moves in and the cable is connected but DVD players and scanners are not the answer.

You are going to have to wait until the actual cable signal is available. The reason for this is your "system" needs to be designed around the level supplied by the CATV drop and it's not a given that it will be the same from house to house.

If you don't have the equipment to determine signal levels simply run and terminate your runs and let the cable company handle the connnections at the home run location.

They will probably want to connect only those runs that actually have a set connected to them anyway so if you install a bunch of splitters to make all jacks "hot" it will likely be a waste of time.

-Hal

I wouldn't even terminate the runs. Let the cable company do that with their preffered connectors.